loxodrom {birdring}

loxodromic distance and direction

Description

calculates the loxodromic distance and direction between two points on the earth

Usage

loxodrom.dir(x1, y1, x2, y2, epsilon = 1e-06)

loxodrom.dist(x1, y1, x2, y2, epsilon = 1e-04, package="geosphere")

Arguments

x1

x-coordinate/longitude of the first point (in decimal coordinates), can be a scalar or a vector

y1

y-coordinate/latitude of the first point (in decimal coordinates), can be a scalar or a vector

x2

x-coordinate/longitude of the second point (in decimal coordinates), can be a scalar or a vector

y2

y-coordinate/latitude of the second point (in decimal coordinates), can be a scalar or a vector

epsilon

a threshold value for considering a number as zero. See details.

package

if "geosphere" (default) the function is based on the geosphere package, if "birdring" the function written by F. Korner is used. The latter is less reliable.

Details

If you use the birdring package, please, check the results carefully, especially when vectors instead of scalars are given as arguments. If some distances or directions are obviously wrong (such cases occurred predominantly when the bird moved exactly into one of the four directions 0, 90, 180 or 270 degrees) then it might help to increase the value of epsilon.

Value

The function loxodrom.dist() gives back a number or a vector with the distances in km between the two points on earth. The function loxodrom.dir() gives back a number or a vector with the directions in degees from North (clockwise) between the two points on earth.

Warning

see details

Author(s)

Fraenzi Korner-Nievergelt

References

Imboden, C., Imboden D. (1972) Orthodromic and loxodromic formula for the calculation of distance and direction between ringing and finding place. Vogelwarte 26: 336-346.

See Also

decimal.coord

Examples

ringingx<-7.30
ringingy<-47.41
findingx<-5.1
findingy<-32.01
rxdec<-decimal.coord(ringingx)
rydec<-decimal.coord(ringingy)
fxdec<-decimal.coord(findingx)
fydec<-decimal.coord(findingy)     

loxodrom.dist(rxdec, rydec, fxdec, fydec) 

loxodrom.dir(rxdec, rydec, fxdec, fydec)